Electro-acoustic transducers



June 13, 1967 S. L. HEIDRICH ELECTRO-ACOUSTIC TRANSD UCERS Filed Oct. 12, 1966 INVENTOR STEPHEN L. HEIDRICH ATTORNEY.

United States l atent 3,324,966 ELECTRO-ACOUSTIC TRANSDUCERS Stephen L. Heidrich, 29 Richmond Drive,

Darien, Conn. 06820 Filed Oct. 12, 1966, Ser. No. 586,240 8 Claims. (Cl. 181-31) The present invention relates to sound translating devices, in general, and in particular, to electro-acoustic transducers, more popularly known as loud speakers, which consist of a loud speaker motor unit of the dynamic or moving coil type operating an acoustic diaphragm, one side of which acts on an enclosed space known as the loud speaker enclosure. The loud speaker enclosure provides an acoustical load on a loud speaker diaphragm, which reacts on the loud speaker motor and opposes the applied power more or less, as determined by the acoustical properties of the enclosure.

. The present invention is directed toward improvements in a loud speaker construction of the completely enclosed or infinite bafiie type containing a resurgent high pressure acoustic system in which a high acoustic resistance is coupled with relatively small acoustic capicitances in response to lower frequencies of the acoustic spectrum of the general type as disclosed in my copend-ing patent application Ser. No. 524,015, filed Feb. 1, 1966, entitled, Electro-Acoustic Transducer.

, In the mentioned copending patent application, there is disclosed a system in which the low frequency response capacity of the infinite bafiie is increased, with a satisfactory decrease in the acoustic capacitance heretofore contained in the enclosure, for very compact loud speakers. This is achieved with an operative acoustic diaphragm mounted in a small housing in which two very small air chambers functioning as air capacitances are interconnected by an extra-ordinarily high acoustic resistance in the form of a high resistance air duct conductor of substantial length relative to its width, which in cooperation withone of the two air capacitances acts as an acoustic resistance-capacitance couple, that reacts favorably to low frequency'cycles of compression and decompression that are impressed via the first chamber from the back of a related acoustic diaphragm.

I The'specific construction disclosed in the mentioned copending patent application consists of an arrangement of contiguous walls forming an air conductor passage which is generally peripheral to the speaker and axially disposed thereto.

This arrangement, although producing decided advantages and excellent tone quality due to the high resistance air duct conductor, required extremely close contiguous spacing between the peripheral walls forming the air conductor passage extending over a range of about one tenth of a thousandth to about one hundred thousandths of an inch. Accordingly, the wall enclosures were precision made and carefully, coaxially aligned.

Generally said copending patent application discloses an electro acoustic transducer for generating acoustic pressure variations to a fluid medium which comprises a housing including a wall and also means for generating acoustic pressure variations to a fluid medium within the housing and disposed within an opening in the wall of the housing, the latter comprising a first enclosure defining a first chamber, a second enclosure defining a second chamber. A first wall of one of said enclosures is disposed contiguous to a second wall of either one of the enclosures and defines a narrow air conductor between the first and 'se'cond walls. The first chamber communicates with the second chamber, and the air conductor is of substantial length relative to the distance between the first and second walls.

It is one object of the present invention to provide small loud speakers having a satisfactory wide frequency range of response with an enclosure, operating as an acoustic buffer unit for low frequencies and which lends itself to simplified and more economical manufacture.

It is another object of the present invention to provide an electr-o-acoustic transducer arrangement for genera-ting pressure variations to a fluid medium consistnig of contiguous wall forming an .annularly radial fluid medium passage disposed perpendicular and radial to the speaker unit. With this arrangement the walls can be mass produced economically without sacrificing precision spacing required between the contiguous walls. Further, two annular chambers are formed about the magnetic structure of the speaker unit permit-ting smaller loud speaker systems.

It is still another object of the present invention to provide an electro-acoustic transducer arrangement in accordance with the previously mentioned objective further comprising spacer means disposed between the contiguous walls to insure the required spacing.

With these and other objects in view which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawings, in which:

FIGURE 1 is an axial section of a loud speaker embodying the feature of the present invention;

FIG. 2 is a front elevation of the loud speaker, the forward portion being partly removed, to show a section on a plane through the first air chamber back of the acous tic diaphgram; and

FIG. 3 is an axial section of another embodiment of the loud speaker.

Referring now to the drawing and in particular to FIGS. 1 and 2, the electro-acoustic transducer comprises a conventional dynamic loud speaker unit 10 consisting of a conical acoustic diaphragm 11 suspended by a compliant peripheral flange 12 cemented to a supporting rim 13 of a basket 14 of a magnetic structure 15 actuated by a voice coil 16 which operates in a magnetic gap 17 in the magnetic structure 15. The dynamic loud speaker 10 is integrated in a housing according to this acoustic device.

The housing comprehends essentially two cooperative members, namely, housing enclosure member 19 which encloses both a first chamber 20 and a second chamber 21 which chambers 20 and 21 are defined by a rigid annular baflle member 18 disposed about the magnetic structure 15 and perpendicular to the housing enclosure member 19.

The housing enclosure member 19 comprises a front cylindrical portion 19a and a rear cylindrical portion 1% respectively enclosing the first chamber 20 and the second chamber 21, respectively. The rear. cylindrical portion 1911 has a smaller radius than that of the front cylindrical portion 19a. In back of the bafiie member 18, the housing enclosure member 19 has a radially inwardly oriented annular wall 22, which joins the front and rear cylindrical port-ions 19a and 1%, respectively, and is overlappingly and slightly spaced apart from a rear radial annular wall 23 of the rigid annular bafiie 18 so as to form an annular, radial air duct 24 between the annular walls 22 and 23, respectively, and interconnecting the chambers 20 and 21. A gasket 25, preferably of rubber is disposed about the front end of the housing enclosure member 19 and the basket 14 or the diaphragm 11.

As clearly disclosed in FIG. 1 of the drawing, the baflle member 18 comprises the radial annular wall 23 which extends radially parallel and contiguous to the annular wall 22 of the housing enclosure member 19 nearly up to, but short of, the front cylindrical portion 19a to define a circumferential orifice 25 at the circumferential edge of the annular wall 23. The magnetic structure 15 is preferably secured to the back wall 19c of the housing enclosure member 19 by a screw 26 and a washer 26a, and the magnetic structure so secured thereby holds the annular baflie member 18 by ring 15a in fixed and spaced relationship relative to the housing enclosure member 19, or the annular baffle member 18 may be free fitted over the magnetic structure 15, thereby, fiber glass packing 27 and 28 provided optionally in the first and second chambers and 21, respectively, which fiber glass packing 27 and 28 optimizes the density for suitable damping. It is to be noted that the annular walls 22 and 23 and chamber connecting duct 24 are oriented perpendicular and intermediate radially relative to the magnetic structure 15, so that the first and second chambers 20 and 21, respectively, are substantially and annularly located with respect to the magnetic structure thereby optimizing space requirements of the system.

Spacing elements 29 are circularly disposed between the annular wall 23 of the baffle member 13 and the annular wall 22 of the housing enclosing member 19 and secured therebetween by fasteners 30 to insure the proper duct spacing.

In operation the movements of the diaphragm 11 impelled by the energized voice coil 16, generate compressions and decompressions of air in the chamber 20 which being of a small volume causes plus and minus pressures to attain exceptionally high degrees about and below the atmospheric pressure and, thereby, provides an air stiffness and control over the movements of the diaphragm 11, which predominates over the mechanical stiffness of the compliances in the diaphragm 11. The air stiffness thereby takes Over much of the inertia of the moving parts.

The air duct conductor 24 slowly releases the higher pressures in the chamber 20, which are generated increasingly with decrease of frequency to the chamber 21, where plus and minus pressures are regenerated again but With a time lag as compared with the pressures prevailing in the first chamber 20 and reach a peak when the incoming air pressures through the air duct conductor 24 become equal to the air pressures in the second chamber 21. The regenerated pressures in the chamber 21, which act as an acoustic butter unit for low frequencies, become immediately resurgent with the reversal of air flow adding the released power of resurgence through this air duct conductor 24 to the back of the acoustic diaphragm 11 at a frequency compatible to that in the acoustic resistance-capacitance couple of the air duct conductor 24 with the air chamber 21.

Because of the small housing desired for this loud speaker, the acoustic capacitance of the chambers 20 and 21 is comparatively minute and the complementary acoustic resistance necessary to achieve a low frequency resurgence of 50 cycles or less is extraordinarily great. The high acoustic resistance is achieved in accordance with the extremely close contiguous radial spacing, that is, in the order of a few thousandths of an inch, extending over a range of about one tenth of a thousandth to about One hundred thousandths of an inch, depending upon the size of the loud speaker, between the annular walls 22 and 23 of the members 18 and 19, respectively, which define the air duct conductor 24, thus providing the means for attaining an extraordinarily high acoustic resistance in the great area of surface viscosity provided as compared to the minute cross sectional area of the duct conductor 24. With the present radial spacing the bafiie member 18 can be economically mass produced. The spacing elements 29 further insure the precision alignment and narrow spacing of the duct 24. With this arrangement there is applied a high pressure by virtue of the small capacitances, resistance controlled acoustic loading system in which the acoustic resistance is very great and is an effective retarding element, as well as of economical construction to the flow of air between the two relatively small chambers. Such high acoustic resist- 4 ance is obtained by the annular air duct 24 of the viscosit effect'of extensive surface area as compared to the crosssectional area of the duct. Accordingly, a high pressure resistance controlled regenerative acoustic loading system is achieved acting on the back of a related acoustic diaphragm, in which a high acoustic resistance is provided in the great viscosity residing in a thin radial air duct conductor formed intermediate the annular contiguous walls of substantial length as compared to the cross sectional area of such air duct conductor.

Referring now again to the drawings, and in particular to FIG. 3, an embodiment is disclosed, which follows substantially the previously disclosed embodiment.

The electro-acoustic transducer comprises again a conventional dynamic loud speaker unit 10' consisting of a conical acoustic diaphragm 11 suspended by a compliant peripheral flange 12 cemented to a supporting rim 13 of a basket 14 of a magnetic structure 15 actuated by a voice coil 16 which operates in a magnetic gap 17 in the magnetic structure 15. The dynamic loud speaker 10' is integrated in a housing or enclosure according to this acoustic device.

While the magnetic structure 15 is substantially identical with the arrangement in the first embodiment, the housing comprises here a preassembled radial acoustic buffer unit 31 consisting of two cooperative, overlapping members 18 and 19, namely a first baflle member 18 defining with the outer housing enclosure 32 a front annular chamber 20 surrounding the front of the magnet structure 15' behind the basket 14, and a second enclosure member 19' defininga rear annular chamber 21' around the back portion of the magnetic structure 15, the first baffle member 18 having a radial annular wall 23' and the second enclosure member 19' having a radial annular wall 22, which walls 22' and 23' radially and annularly overlap close to each other. The walls 22' and 23' are spaced apart, so as to form an air duct 24' with the same characteristics as duct 24 of FIG. 1. The members 18' and 19, defining the acoustic buffer unit for low frequencies, are surrounded by the outer enclosure 32, which is preferably formed of separate members, which are sealingly joined together, and which receives the magnetic structure 15', and defines the chamber 20 communicating with the chamber 21' in the same manner as described in the description of the first embodiment. The second chamber enclosure 19 includes a circular rear wall 33, radially extending beyond the circumferential edges of magnetic structure 15, a cylindrical wall 34 and the radial annular wall 22 which depends radially inward toward the magnetic structure 15' but terminating short thereof/The radial distance inward through which the wall 22 extends determines the length of the air duct 24-. Thebaffle member 18 includes a circular wall 35 of smaller radius than that of the rear wall 33 of the second chamber enclosure 19, but of a radius slightly larger than that of the magnetic structure 15. From the edge of the circular wall 35 forwardly extends a cylindrical wall 36 of length slightly longer than the length of the cylindrical wall 34 of the second chamber enclosure 19, which slightly larger length precisely determines the spacing of the radial duct 24. From the front end of the cylindrical wall 36, annular wall 23' extends to about the radius of the cylindrical wall 34 of the second chamber enclosure 19. The first and second members 18 and 19, respectively, are secured by central screw 26 which holds the circular Walls 35 and 33 of the first and second chamber enclosures, respectively, togeher, and with rubber washer 26'a to the magnetic structure 15.

It should be noted'that the length of annular wall 22 of the second chamber enclosure 19' and the length of the cylindrical wall 36 of the first baffle member 18 beyond the cylindrical wall 34, precisely determines the substantial length to width ratio of the air duct 24 necessary for the proper functioning of the transducer. Spacing elements 29 as in the embodiment of FIG. 1 are dis posed circumferentially around and between the radial walls 22' and 23 and held by fasteners 30 thereby establishing the integrity of the duct spacing.

Whereas the present invention constitutes an improvement in the construction of a compact loud speaker of the type described in my copending patent application heretofore indicated, and preferred embodiments of the construction have been disclosed, it is to be understood that other embodiment are possible and that the scope of the present invention includes any acoustic device employing an operative acoustic diaphragm, the back of which acts on a system of two small interconnected chambers in which the generated and regenerated acoustical resurgencies from one to the other one controlled by a dominatingly high acoustic resistance in an air duct conductor defined by radially disposed wall surfaces of an extensive area, as compared with the cross-sectional area of said duct conductor. It is further understood that the term air is analogous with any fluid medium and the use of lighter or heavier than air fluid mediums in the resistancecapacitance system described, are within the scope of the present invention, which is defined by the object-s and the claims.

While I have disclosed several embodiments of the present invention, as applied to loudspeakers, it is to be understood that these embodiments are given by example only and not in a limiting sense, as the same invention is applicable to microphones and hearing aids, the scope of the present invention being determined by the objects and the claims.

I claim:

1. An electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, comprising a housing including a wall,

means for generating acoustic pressure variations to a fluid medium within said housing and disposed within an opening in said wall of said housing, said housing comprising a first enclosure and a second enclosure cooperatively spaced defining a first chamber and a second chamber, respectively,

a first radial wall of one of said enclosures being disposed radially contiguous to a second radial wall of either one of said enclosures and defining a narrow radial air duct conductor between said first and second radial Walls,

said first chamber communicating with said second chamber through said radial air duct conductor, and

said radial air duct conductor being of substantial radial length relative to the axial distance between said first and second radial walls.

2. The electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 1, further comprising spacer means disposed between said first and second radial walls.

3. The electro-acoutic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 1, wherein said first radial wall of said first enclosure is disposed radially contiguous to said second radial wall of said second enclosure.

4. The electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 1, wherein said first radial Wall of said second enclosure is disposed radially contiguous to said second radial wall of said second enclosure.

5. The electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 1, wherein said first radial wall and said second radial will constitute annularly shaped walls having inner and outer circumferential edges, respectively,

said first radial wall disposed about and perpendicularly to said acoustic pressure generating means, thereby locating said first and second chambers generally annularly about said acoustic pressure generating means, and

said second radial wall extending from about the outer circumferential edge of said first radial wall to a distance short of the inner circumferential edge of said first radial wall.

6. The electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 5, wherein said first chamber covers the back of said acoustic pressure generating means and said second chamber ber backs up on said first chamber,

said first radial wall forming the back of said first chamber except for a space adjacent the outer circumferential edge of said first radial wall,

said second radial wall is disposed adjacent the front of said second chamber,

said inner and outer circumeferential edges of said radial walls, respectively, defining ends which are open to said first chamber and said second chamber, respectively,

said radial air duct conductor connecting said two chambers between said ends, and

said radial air duct conductor having sufiicient acoustic resistance to act as a brake on the movements of said acoustic diaphragm, when operated at the lower frequencies of the audio spectrum.

7. The electro-acoustic transducer for generating acoustic pressure variations to a fluid medium, as set forth in claim 5, wherein said first enclosure constitutes an annular baflie including said first radial wall, and

said housing including said second enclosure.

8. The electro-acoustic transducer for generating acoustic pressure variations to a fliud medium, as set forth in claim 7, wherein said first member is disposed within said housing and radially divides said housing into first and second chambers,

said housing is substantially circular in cross-section and having a first cylindrical portion about said first chamber and a second cylindrical portion about said second chamber, the radius of said second cylindrical portion being smaller than the radius of said first cylindrical portion, and

said second radial wall of said second enclosure joining said first cylindrical portion with said second cylindrical portion.

References Cited UNITED STATES PATENTS 1,837,755 12/1931 Carlisle et al. 181--31 2,065,751 12/1936 Scheldorf 1813 1 2,217,279 10/1940 Karns 181--31 2,766,839 10/1956 Baruch et al 18 l31 2,957,954 10/1960 Swinehart 1791 10 FOREIGN PATENTS 971,517 7/1950 France.

1,065,126 12/1953 France.

STEPHEN I. TOMSKY, Primary Examiner. 

1. AN ELECTRO-ACOUSTIC TRANSDUCER FOR GENERATING ACOUSTIC PRESSURE VARIATIONS TO A FLUID MEDIUM, COMPRISING A HOUSING INCLUDING A WALL, MEANS FOR GENERATING ACOUSTIC PRESSURE VARIATIONS TO A FLUID MEDIUM WITHIN SAID HOUSING AND DISPOSED WITHIN AN OPENING IN SAID WALL OF SAID HOUSING, SAID HOUSING COMPRISING A FIRST ENCLOSURE AND A SECOND ENCLOSURE COOPERATIVELY SPACED DEFINING A FIRST CHAMBER AND A SECOND CHAMBER, RESPECTIVELY, A FIRST RADIAL WALL OF ONE OF SAID ENCLOSURES BEING DISPOSED RADIALLY CONTIGUOUS TO A SECOND RADIAL WALL OF EITHER ONE OF SAID ENCLOSURES AND DEFINING A NARROW RADIAL AIR DUCT CONDUCTOR BETWEEN SAID FIRST AND SECOND RADIAL WALLS, SAID FIRST CHAMBER COMMUNICATING WITH SAID SECOND CHAMBER THROUGH SAID RADIAL AIR DUCT CONDUCTOR, AND SAID RADIAL AIR DUCT CONDUCTOR BEING OF SUBSTANTIAL RADIAL LENGTH RELATIVE TO AXIAL DISTANCE BETWEEN SAID FIRST AND SECOND RADIAL WALLS. 